model 3 LFP battery charging efficiency

[ltarca]

I wonder for the model 3 LFP and level 2 charger, how does efficiency vs. charging amps look like? Is it more efficient to charge at 32A or say 20A ?

 

[dhrivnak]

I can’t imagine a difference. That said I charge at a slowish 24A as I try to match solar output, I figure it is easier for the power company and I am still always full by morning.

 

[jcanoe]

Once you move to 240V charging the difference in efficiency between using a circuit rated between 20A and up to 50A would be very small. I have read that charging at 48A using a 60A circuit is slightly less efficient. This may be due to needing additional cooling of the on-board charger during the charging session when charging at 11.5kW.

As far as Supercharging there were some tests performed on Model 3 SR vehicles with the LFP battery that showed some differences in charging time as compared to the lithium ion battery packs. Tesla later revised the charging algorithm for the LFP Model 3 when Supercharging that may have improved the charging time.

 

[ltarca]

thank you both. I would assume that depending on the outside temperature, when charging time is not an issue (e.g. over night charging), there must be an optimal Amp level for charging.

 

[jcanoe]

thank you both. I would assume that depending on the outside temperature, when charging time is not an issue (e.g. over night charging), there must be an optimal Amp level for charging.

The highest charging amperage and charging rate (in kW) would result in the shortest and therefore most efficient charging session. If the 48A charging rate is not the most efficient due to additional cooling of the on-board charger, etc. then the 40A charging rate would be the next highest, optimal charging rate.

 

[JimOdbe]

The highest charging amperage and charging rate (in kW) would result in the shortest and therefore most efficient charging session. If the 48A charging rate is not the most efficient due to additional cooling of the on-board charger, etc. then the 40A charging rate would be the next highest, optimal charging rate.

Not really. I^2*R losses are larger at higher amperages. I noticed my line from the breaker to the 240V outlet actually felt warm when charging at 32A, which got me thinking. If I cut the charging rate to 16A, I reduce the I^2R losses by 75%. I assume there are equivalent losses in the car internals, so this could be significant. I do not see why "shortest and therefore most efficient" is valid. Is gunning a gas car all the way to the store more or less efficient than driving at a normal speed? The drive is shorter, but certainly not more efficient.

 

[jcanoe]

Not really. I^2*R losses are larger at higher amperages. I noticed my line from the breaker to the 240V outlet actually felt warm when charging at 32A, which got me thinking. If I cut the charging rate to 16A, I reduce the I^2R losses by 75%. I assume there are equivalent losses in the car internals, so this could be significant. I do not see why "shortest and therefore most efficient" is valid. Is gunning a gas car all the way to the store more or less efficient than driving at a normal speed? The drive is shorter, but certainly not more efficient.

When the Tesla Model Y is charging the electronics are powered on, consuming ~230W. That overhead is constant while the vehicle is powered on. If you can complete charging in 2 hours instead of 4 hours then charging overhead would use almost half a kWh less energy for the charging session.